1. Field of the Invention
The present invention relates to polyblend compositions comprising a vinyl chloride polymer (PVC) and a polyolefin and to the use of such polyblends for applications which require rheological properties and fire resistance which are compatible with the production of molded shaped articles and objects, for example cases, covers and frames employed in the field of office equipment.
2. Description of the Prior Art
The conventional techniques for converting polyblend compositions include, for example, extrusion, blow extrusion, calendaring, thermoforming, injection molding and others. These techniques require a composition having sufficient fluidity when heated.
Polymeric resins which have high-performance mechanical properties and which intrinsically have a high fire resistance are known to this art for the production of such molded shaped articles and objects.
PVC is acknowledged to be an excellent material in this respect. However, this polymer presents a certain number of disadvantages, especially a poor injectability when its fluidity values K range from 54 to 70.
Injection presses fitted with screws which have highly specific profiles must be employed, and these are of a type likely to retard the development of the aforesaid shaped articles which are molded on standard presses.
To remedy this disadvantage, mixtures of PVC with various thermoplastic polymers have heretofore been formulated, especially with polyolefins serving to lower the melt viscosity of the PVC and, consequently, making it easier to convert the mixtures thus formulated, especially by injection molding.
Although the mixtures obtained have a suitable melt viscosity for the application of the above indicated conversion techniques, the compatibility of their constituents is reduced. The adhesion between the disperse phase and the matrix is poor and during conversion of these mixtures a marked decrease in the mechanical properties and a delamination are observed, effectively precluding their use for a wide variety of intended applications.